Are there any signs that people may have before if they die?

I'm 15 and I have this little feeling that I would die soon after a few years because of my constipation problems. I've been having it for two years already and have tried almost everything. My parents don't really care too much or know much how to cure it. So are there any signs before death? I didn't have any symptoms or pain these two years. Just uncomfortable. Like heavier breathing?When I was 10, I used to believe that when a person almost dies, they would have heavier breathing. Right now I think my breathing has gotten heavier.